This application claims the priority of German patent document 197 11 739.2 filed Mar. 20, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a governor for air compressors of vehicles, said compressors comprising at least one compressor, a compressed air storage tank that can be charged by the compressor, and an additional device that can be switched when a set pressure level is reached in the compressed air storage tank, especially for compressed air braking systems of road vehicles. An inlet connection is subjected to the pressure in the compressed air storage tank and a housing has an outlet connection that conducts an outlet pressure, with the outlet connection being connected with the additional device to switch it.
Governors of this kind, both when a lower pressure limit of the regulated pressure provided for the compressed air storage tank falls below atmospheric pressure and when an upper pressure level of the regulated pressure is exceeded, deliver an overpressure corresponding to the pressure in the tank at the outlet connection; this pressure at the outlet connection is used as a switching pressure for the additional device. The additional device can be a piston-controlled outlet valve for venting the air delivered by the compressor to atmosphere during compressor idle phases, an energy-saving device for the air compressor, for example a device to hold the compressor inlet valve open or a valve of a "damage area" regulator for the compressor that is separate and is installed in parallel with the compressor inlet valve, an intake throttle in the air intake manifold of the compressor, a shutoff clutch in the compressor rotary drive, an air drying device, especially a regeneration switching device therefor, or the like, individually or combined in a system.
Known governors have a regulating piston that is urged by a regulating spring against the pressure in a compressed air storage tank, said piston, when subjected to pressure that reaches a regulated pressure level, opening an inlet valve to connect the compressed air storage tank with the outlet connection, while when the piston is subjected to a lower pressure, it closes this valve and opens an outlet valve to connect the outlet connection with the atmosphere; the two valves are then combined into a double valve.
In this known governor design, the total quantity of air that the additional devices require for switching must flow through the valves that can be switched by the control piston, and therefore the valves must be designed with large cross sections, but this results in insensitive and inaccurate switching behavior; thus, only an unsatisfactory compromise involving rapid switching of the additional devices on the one hand and sufficient switching accuracy on the other hand can be achieved, with the variable quantity of compressed air required by the additional devices for switching possibly producing further undesired changes in switching behavior. As a result, an undetermined time-delayed switching behavior of the additional devices can result, with undesired or even inadmissibly excessive or reduced pressure in the compressed air supply tank. There is also the danger that the valves will be opened by the switching piston only gradually or only partially, which can result in incomplete switching of the additional devices, with correspondingly serious consequences: overloading or underloading of the compressed air supply tank; constant, unnecessary losses of compressed air and therefore of energy because exhaust valves are only partially open; failure of the air-drying devices to function; excessive wear and overheating of the shutoff clutch, and/or harmful vibration in the compressed air system or compressor drive.
Commonly assigned German patent application DE-A1-2949434 teaches a pressure regulator that is sold under the model designation DR 35 for air compressors for commercial vehicles. That pressure regulator acts on an outlet connection, said connection being maintained by an adjustable regulating spring against the pressure in an outlet connection possibly to be connected with a compressed air supply tank through an air dryer. The regulating piston is connected with a valve tube of a round slide valve, said valve, with predominant loading of the regulating piston by the pressure in the outlet connection, venting a loading chamber to atmosphere, and with insufficient loading, connecting the loading chamber with the outlet connection by shutting off this vent. The loading chamber is bounded by a switching piston, said piston, when the loading chamber is pressurized, opening to the atmosphere an otherwise closed outlet valve with a large cross section from an inlet connection connected with the compressor. The regulating piston with the slide valve and the switching piston with the outlet valve are mounted coaxially in a housing. The slide valve has a "dead stroke," causing it to acquire switching hysteresis so that it connects the loading chamber with the atmosphere on reaching an upper pressure limit for a regulated pressure level in the outlet connection, and connects it with the outlet connection when the regulated pressure level falls below a lower pressure limit.
An object of the invention is to design a governor in simple fashion such that regardless of the switching-air requirement of the additional device or devices, the latter is or are switched in a functionally reliable fashion, always exactly and completely, with the correct pressure level in the air compressor.
This and other objects have been achieved according to the present invention by providing a governor for a system including at least one compressor, a compressed air supply tank chargeable by the compressor, and an additional device that can be switched when a regulated pressure level is reached in the compressed air supply tank, comprising: a housing having an inlet connection communicating with the compressed air supply tank, and having an outlet connection communicated with the additional device; a pilot valve arranged in the housing; and a relay valve arranged in the housing, said relay valve having a cross section which is larger than a cross section of the pilot valve, said relay valve being pneumatically controlled by said pilot valve to set the outlet pressure at outlet connection when a pressure limit is exceeded in the inlet connection.
The present invention utilizes a pilot valve with a small cross section, located in the housing. This pilot valve, when a pressure limit is exceeded in the inlet connection, pneumatically controls a relay valve with a large cross section located in the housing to set the pressure at the outlet connection. Such governors can be used in air compressors, especially in conjunction with compressors and air dryers for commercial vehicles.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.